Methods to partially reduce a niobium metal oxide and oxygen reduced niobium oxides

ABSTRACT

Methods to at least partially reduce a niobium oxide are described wherein the process includes heat treating the niobium oxide in the presence of a getter material and in an atmosphere which permits the transfer of oxygen atoms from the niobium oxide to the getter material, and for a sufficient time and at a sufficient temperature to form an oxygen reduced niobium oxide. Niobium oxides and/or suboxides are also described as well as capacitors containing anodes made from the niobium oxides and suboxides.

[0001] This application is a continuation-in-part of U.S. patentapplication Ser. No. 09/533,430 filed Mar. 23, 2000 and also is acontinuation-in-part of U.S. patent application Ser. No. 09/347,990filed Jul. 6, 1999, and U.S. patent application Ser. No. 09/154,452filed Sep. 16, 1998, which are all incorporated herein in their entiretyby reference.

BACKGROUND OF THE INVENTION

[0002] The present invention relates to niobium and oxides thereof andmore particularly relates to niobium oxides and methods to at leastpartially reduce niobium oxide and further relates to oxygen reducedniobium.

SUMMARY OF THE PRESENT INVENTION

[0003] In accordance with the purposes of the present invention, asembodied and described herein, the present invention relates to a methodto at least partially reduce a niobium oxide which includes the steps ofheat treating the niobium oxide in the presence of a getter material andin an atmosphere which permits the transfer of oxygen atoms from theniobium oxide to the getter material for a sufficient time andtemperature to form an oxygen reduced niobium oxide.

[0004] The present invention also relates to oxygen reduced niobiumoxides which preferably have beneficial properties, especially whenformed into an electrolytic capacitor anode. For instance, a capacitormade from the oxygen reduced niobium oxide of the present invention canhave a capacitance of up to about 200,00° CV/g or more. Further,electrolytic capacitor anodes made from the oxygen reduced niobiumoxides of the present invention can have a low DC leakage. For instance,such a capacitor can have a DC leakage of from about 0.5 nA/CV to about5.0 nA/CV.

[0005] Accordingly, the present invention also relates to methods toincrease capacitance and reduce DC leakage in capacitors made fromniobium oxides, which involves partially reducing a niobium oxide byheat treating the niobium oxide in the presence of a getter material andin an atmosphere which permits the transfer of oxygen atoms from theniobium oxide to the getter material, for a sufficient time andtemperature to form an oxygen reduced niobium oxide, which when formedinto a capacitor anode, has reduced DC leakage and/or increasedcapacitance.

[0006] The present invention further relates to capacitor anodescontaining the niobium oxides of the present invention and having otherbeneficial properties.

[0007] It is to be understood that both the foregoing generaldescription and the following detailed description are exemplary andexplanatory only and are intended to provide further explanation of thepresent invention, as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

[0008] FIGS. 1-11 are SEMs of various oxygen reduced niobium oxides ofthe present invention at various magnifications.

[0009]FIG. 12 is a graph plotting DC leakage vs. Formation voltage for aniobium oxide capacitor anode and other anodes made from niobium ortantalum.

[0010]FIGS. 13 and 14 are graphs showing a DCL and capacitancecomparison of an anode containing niobium oxide compared to anodescontaining niobium flake and tantalum.

[0011]FIG. 15 is a graph showing DC leakage for anodes formed fromniobium suboxides of the present invention.

[0012]FIG. 16 is a graph showing the capacitance from a wet anodesformed from niobium oxide and tantalum.

[0013]FIGS. 17 and 18 are graphs showing the flammability of anodes fromniobium, tantalum, and niobium oxide.

[0014]FIG. 19 is a graph showing the ignition energy needed to igniteniobium oxide powders compared to niobium powders and tantalum powders.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0015] In an embodiment of the present invention, the present inventionrelates to methods to at least partially reduce a niobium oxide. Ingeneral, the method includes the steps of heat treating a startingniobium oxide in the presence of a getter material in an atmospherewhich permits the transfer of oxygen atoms from the niobium oxide to thegetter material for a sufficient time and at a sufficient temperature toform an oxygen reduced niobium oxide.

[0016] For purposes of the present invention, the niobium oxide can beat least one oxide of niobium metal and/or alloys thereof. A specificexample of a starting niobium oxide is Nb₂O₅.

[0017] The niobium oxide used in the present invention can be in anyshape or size. Preferably, the niobium oxide is in the form of a powderor a plurality of particles. Examples of the type of powder that can beused include, but are not limited to, flaked, angular, nodular, andmixtures or variations thereof. Preferably, the niobium oxide is in theform of a powder which more effectively leads to the oxygen reducedniobium oxide.

[0018] Examples of such preferred niobium oxide powders include thosehaving mesh sizes of from about 60/100 to about 100/325 mesh and fromabout 60/100 to about 200/325 mesh. Another range of size is from −40mesh to about −325 mesh.

[0019] The getter material for purposes of the present invention is anymaterial capable of reducing the specific starting niobium oxide to theoxygen reduced niobium oxide. Preferably, the getter material comprisestantalum, niobium, or both. More preferably, the getter material isniobium. The niobium getter material for purposes of the presentinvention is any material containing niobium metal which can remove orreduce at least partially the oxygen in the niobium oxide. Thus, theniobium getter material can be an alloy or a material containingmixtures of niobium metal with other ingredients. Preferably, theniobium getter material is predominantly, if not exclusively, niobiummetal. The purity of the niobium metal is not important but it ispreferred that high purity niobium metal comprise the getter material toavoid the introduction of other impurities during the heat treatingprocess. Accordingly, the niobium metal in the niobium getter materialpreferably has a purity of at least about 98% and more preferably atleast about 99%. Further, it is preferred that impurities such as oxygenare not present or are present in amounts below about 100 ppm.

[0020] The getter material can be in any shape or size. For instance,the getter material can be in the form of a tray which contains theniobium oxide to be reduced or can be in a particle or powder size.Preferably, the getter materials are in the form of a powder in order tohave the most efficient surface area for reducing the niobium oxide. Thegetter material, thus, can be flaked, angular, nodular, and mixtures orvariations thereof. The getter material can be a tantalum hydridematerial. A preferred form is coarse chips, e.g., 14/40 mesh chips thatcan be easily separated from the powder product by screening.

[0021] Similarly, the getter material can be tantalum and the like andcan have the same preferred parameters and/or properties discussed abovefor the niobium getter material. Other getter materials can be usedalone or in combination with the tantalum or niobium getter materials.Also, other materials can form a part of the getter material.

[0022] Generally, a sufficient amount of getter material is present toat least partially reduce the niobium oxide being heat treated. Further,the amount of the getter material is dependent upon the amount ofreducing desired to the niobium oxide. For instance, if a slightreduction in the niobium oxide is desired, then the getter material willbe present in a stoichemetric amount. Similarly, if the niobium oxide isto be reduced substantially with respect to its oxygen presence, thenthe getter material is present in a 2 to 5 times stoichemetric amount.Generally, the amount of getter material present (e.g., based on thetantalum getter material being 100% tantalum) can be present based onthe following ratio of getter material to the amount of niobium oxidepresent of from about 2 to 1 to about 10 to 1.

[0023] Furthermore, the amount of getter material can also be dependenton the type of niobium oxide being reduced. For instance, when theniobium oxide being reduced is Nb₂O₅, the amount of getter material ispreferably 5 to 1.

[0024] The heat treating that the starting niobium oxide is subjected tocan be conducted in any heat treatment device or furnace commonly usedin the heat treatment of metals, such as niobium and tantalum. The heattreatment of the niobium oxide in the presence of the getter material isat a sufficient temperature and for a sufficient time to form an oxygenreduced niobium oxide. The temperature and time of the heat treatmentcan be dependent on a variety of factors such as the amount of reductionof the niobium oxide, the amount of the getter material, and the type ofgetter material as well as the type of starting niobium oxide.Generally, the heat treatment of the niobium oxide will be at atemperature of from less than or about 800° C. to about 1900° C. andmore preferably from about 1000° C. to about 1400° C., and mostpreferably from about 1200° C. to about 1250° C. In more detail, whenthe niobium oxide is a niobium containing oxide, the heat treatmenttemperatures will be from about 1000° C. to about 1300° C., and morepreferably from about 1200° C. to about 1250° C. for a time of fromabout 5 minutes to about 100 minutes, and more preferably from about 30minutes to about 60 minutes. Routine testing in view of the presentapplication will permit one skilled in the art to readily control thetimes and temperatures of the heat treatment in order to obtain theproper or desired reduction of the niobium oxide.

[0025] The heat treatment occurs in an atmosphere which permits thetransfer of oxygen atoms from the niobium oxide to the getter material.The heat treatment preferably occurs in a hydrogen containing atmospherewhere is preferably just hydrogen. Other gases can also be present withthe hydrogen, such as inert gases, so long as the other gases do notreact with the hydrogen. Preferably, the hydrogen atmosphere is presentduring the heat treatment at a pressure of from about 10 Torr to about2000 Torr, and more preferably from about 100 Torr to about 1000 Torr,and most preferably from about 100 Torr to about 930 Torr. Mixtures ofH₂ and an inert gas such as Ar can be used. Also, H₂ in N₂ can be usedto effect control of the N₂ level of the niobium oxide.

[0026] During the heat treatment process, a constant heat treatmenttemperature can be used during the entire heat treating process orvariations in temperature or temperature steps can be used. Forinstance, hydrogen can be initially admitted at 1000° C. followed byincreasing the temperature to 1250° C. for 30 minutes followed byreducing the temperature to 1000° C. and held there until removal of theH₂ gas. After the H₂ or other atmosphere is removed, the furnacetemperature can be dropped. Variations of these steps can be used tosuit any preferences of the industry.

[0027] The oxygen reduced niobium oxides can also contain levels ofnitrogen, e.g., from about 100 ppm to about 80,000 ppm N₂ or to about130,000 ppm N₂. Suitable ranges includes from about 31,000 ppm N₂ toabout 130,000 ppm N₂ and from about 50,000 ppm N₂ to about 80,000 N₂.

[0028] The oxygen reduced niobium oxide is any niobium oxide which has alower oxygen content in the metal oxide compared to the starting niobiumoxide. Typical reduced niobium oxides comprise NbO, NbO_(0.7),NbO_(1.1), NbO₂, and any combination thereof with or without otheroxides present. Generally, the reduced niobium oxide of the presentinvention has an atomic ratio of niobium to oxygen of about 1:less than2.5, and preferably 1:2 and more preferably 1:1.1, 1:1, or 1:0.7. Putanother way, the reduced niobium oxide preferably has the formulaNb_(x)O_(y), wherein Nb is niobium, x is 2 or less, and y is less than2.5x. More preferably x is 1 and y is less than 2, such as 1.1, 1.0,0.7, and the like.

[0029] The starting niobium oxides can be prepared by calcining at 1000°C. until removal of any volatile components. The oxides can be sized byscreening. Preheat treatment of the niobium oxides can be used to createcontrolled porosity in the oxide particles.

[0030] The reduced niobium oxides of the present invention alsopreferably have a microporous surface and preferably have a sponge-likestructure, wherein the primary particles are preferably 1 micron orless. The SEMs further depict the type of preferred reduced niobiumoxide of the present invention. As can be seen in thesemicrophotographs, the reduced niobium oxides of the present inventioncan have high specific surface area, and a porous structure withapproximately 50% porosity. Further, the reduced niobium oxides of thepresent invention can be characterized as having a preferred specificsurface area of from about 0.5 to about 10.0 m²/g, more preferably fromabout 0.5 to 2.0 m²/g, and even more preferably from about 1.0 to about1.5 m²/g. The preferred apparent density of the powder of the niobiumoxides is less than about 2.0 g/cc, more preferably, less than 1.5 g/ccand more preferably, from about 0.5 to about 1.5 g/cc.

[0031] The various oxygen reduced niobium oxides of the presentinvention can be further characterized by the electrical propertiesresulting from the formation of a capacitor anode using the oxygenreduced niobium oxides of the present invention. In general, the oxygenreduced niobium oxides of the present invention can be tested forelectrical properties by pressing powders of the oxygen reduced niobiumoxide into an anode and sintering the pressed powder at appropriatetemperatures and then anodizing the anode to produce an electrolyticcapacitor anode which can then be subsequently tested for electricalproperties.

[0032] Accordingly, another embodiment of the present invention relatesto anodes for capacitors formed from the oxygen reduced niobium oxidesof the present invention. Anodes can be made from the powdered form ofthe reduced oxides in a similar process as used for fabricating metalanodes, i.e., pressing porous pellets with embedded lead wires or otherconnectors followed by optional sintering and anodizing. The leadconnector can be embedded or attached at any time before anodizing.Anodes made from some of the oxygen reduced niobium oxides of thepresent invention can have a capacitance of from about 1,000 CV/g orlower to about 300,000 CV/g or more, and other ranges of capacitance canbe from about 20,000 CV/g to about 300,000 CV/g or from about 62,000CV/g to about 200,000 CV/g and preferably from about 60,000 to 150,000CV/g. In forming the capacitor anodes of the present invention, asintering temperature can be used which will permit the formation of acapacitor anode having the desired properties. The sintering temperaturewill be based on the oxygen reduced niobium oxide used. Preferably, thesintering temperature is from about 1200° C. to about 1750° C. and morepreferably from about 1200° C. to about 1400° C. and most preferablyfrom about 1250° C. to about 1350° C. when the oxygen reduced niobiumoxide is an oxygen reduced niobium oxide.

[0033] The anodes formed from the niobium oxides of the presentinvention are preferably formed at a voltage of about 35 volts andpreferably from about 6 to about 70 volts. When an oxygen reducedniobium oxide is used, preferably, the forming voltages are from about 6to about 50 volts, and more preferably from about 10 to about 40 volts.Other high formation voltages can be used such as from about 70 volts toabout 130 volts. The DC leakage achieved by the niobium oxides of thepresent invention have provided excellent low leakage at high formationvoltages. This low leakage is significantly better than capacitorsformed with Nb powder as can be seen in, for instance, FIG. 12. Anodesof the reduced niobium oxides can be prepared by fabricating a pellet ofNb₂O₅ with a lead wire followed by sintering in H₂ atmosphere or othersuitable atmosphere in the proximity of a getter material just as withpowdered oxides. In this embodiment, the anode article produced can beproduced directly, e.g., forming the oxygen reduced valve metal oxideand an anode at the same time. Also, the anodes formed from the oxygenreduced niobium oxides of the present invention preferably have a DCleakage of less than about 5.0 nA/CV. In an embodiment of the presentinvention, the anodes formed from some of the oxygen reduced niobiumoxides of the present invention have a DC leakage of from about 5.0nA/CV to about 0.50 nA/CV.

[0034] The present invention also relates to a capacitor in accordancewith the present invention having a niobium oxide film on the surface ofthe capacitor. Preferably, the film is a niobium pentoxide film. Themeans of making metal powder into capacitor anodes is known to thoseskilled in the art and such methods such as those set forth in U.S. Pat.Nos. 4,805,074, 5,412,533, 5,211,741, and 5,245,514, and EuropeanApplication Nos. 0 634 762 A1 and 0 634 761 A1, all of which areincorporated in their entirety herein by reference.

[0035] The capacitors of the present invention can be used in a varietyof end uses such as automotive electronics, cellular phones, computers,such as monitors, mother boards, and the like, consumer electronicsincluding TVs and CRTs, printers/copiers, power supplies, modems,computer notebooks, disc drives, and the like.

[0036] Preferably, the niobium suboxide of the present invention is aNbO or oxygen depleted NbO or an aggregate or agglomerate which containsNbO and niobium metal or niobium metal with a rich oxygen content.Unlike NbO, NbO₂ is undesirable due to its resistive nature, whereas NbOis very conductive. Accordingly, capacitor anodes which are formed fromNbO or oxygen depleted NbO or a mixture of NbO with niobium metal aredesirable and preferred for purposes of the present invention.

[0037] In making the niobium oxides of the present invention, andpreferably NbO or variations thereof, hydrogen gas is preferably used asthe carrier wherein oxygen is transferred from the starting niobiummaterial, namely Nb₂O₅ to Nb with the use of the H₂ gas as the carrier.The preferred reaction scheme is as follows:

[0038] As can be seen, using a niobium metal as the getter material, thegetter material along with the starting niobium oxide can all resultinto the final product which is preferably NbO. In more detail, thereare typically two processes involved in preparing the niobium suboxidesof the present invention. One process involves the preparation of thegetter material and the other part of the process involves the use ofthe getter material along with the starting niobium oxide to form theniobium suboxide of the present invention. In preparing the gettermaterial, which is preferably niobium powder, a niobium ingot issubjected to a hydriding process in order to harden the niobium metalfor purposes of crushing the ingot into powder which is subsequentlysubjected to a screen in order to obtain a uniform particle distributionwhich is preferably from about 5 to about 300 microns in size. Ifneeded, the powder can be subjected two or more times to the crusher inorder to achieve the desired uniform particle distribution. Afterwards,the powder is then subjected to milling in order to obtain the desiredparticle size which is from about 1 to about 5 microns in size. Aftermilling, the material is preferably leached with acid in order to removeimpurities and then the material is subjected to drying to obtain theniobium getter powder.

[0039] This niobium getter powder is then mixed with or blended with thestarting niobium oxide material, which is preferably Nb₂O₅, andsubjected to a hydrogen heat treatment which preferably occurs at atemperature of from about 900 to about 1,200 with the hydrogen pressurebeing from about 50 Torr to about 900 Torr. Preferably, the startingniobium oxide is −325 mesh. Preferably, the heat treatment occurs for asufficient time to achieve the reaction set forth above which is thefull conversion of the getter material and the starting metal oxide tothe final product which is preferably NbO. Thus, in this process, thegetter material as well as the starting metal oxide all become the finalproduct.

[0040] The sintering properties of the anode formed from the niobiumsuboxides of the present invention show that the present inventionprovides an anode which has DC leakage capability comparable to tantalumwhen sintered at high temperatures but, unlike other metals, is lessprone to capacitance lost during sintering. These favorable propertiesare set forth in FIGS. 13 and 14 which show a comparison of thepreferred niobium oxide of the present invention compared to an anodeformed from niobium flake and an anode formed from tantalum. As can beseen in FIG. 13, the anode formed from the niobium oxide of the presentinvention showed satisfactory DC leakage when the anode was sintered attemperatures of from about 1200 to 1600° C. or higher whereas an anodeformed from niobium metal showed a higher DC leakage for sinteringtemperatures of from about 1200 to 1600° C. with no significant drop inDC leakage at high temperatures, such as 1400 to 1600° C.

[0041] Also, as shown in FIG. 14, when an anode made from niobium metalwas sintered at temperatures of from 1200 to 1600° C. and thencapacitance tested with a wet anode, the capacitance steadily declinedas the sintering temperature increased to the point where thecapacitance was about 10,000 CV/g at a sintering temperature of about1600° C. Unlike niobium metal, when an anode made from the niobiumsuboxides of the present invention was tested, the capacitance wasfairly steady when sintered at a variety of temperatures of from 1200 toabout 1600° C. There was only a slight drop at these highertemperatures. This is even different from an anode made from tantalumwhich showed a significant drop after sintering at 1400° C.

[0042] Accordingly, the anodes formed from the niobium suboxides of thepresent invention showed excellent resistance to DC leakage as well asan ability to resist capacitance loss at higher sintering temperatures.

[0043] The anodes formed from the niobium suboxides of the presentinvention further showed an ability to have a low DC leakage even withhigh formation voltages. In addition, the capacitance of the anodesformed from the niobium suboxides of the present invention showed highcapacitance for a variety of formation voltages such as from 20 to 60volts.

[0044] In more detail, as shown in FIG. 15 of the present application,when anodes formed from the niobium suboxides of the present inventionwere tested for DC leakage, the DC leakage was below 10 nA/CV forformation voltages from under 20 to over 60 volts which is quitedifferent from anodes formed from niobium metal which show a dramaticincrease in DC leakage when formation voltages exceeded 50 volts.Further, as shown in FIG. 16, the capacitance from a wet anode formedfrom niobium oxide was comparable to tantalum at formation voltages offrom 20 to 60 volts. These tests and FIGS. 15 and 16 show that theniobium suboxides can be formed into anodes and be used in capacitorsrated up to 20 volts unlike capacitors using niobium metal which arerated below 10 volts.

[0045] In addition, as shown in FIGS. 17 and 18, anodes formed fromniobium suboxides are far less flammable than anodes formed from niobiumor tantalum. As FIG. 17 shows, the heat released from an anode formedfrom the niobium suboxides of the present invention is considerablylower with regard to heat released at 500° C. than tantalum and niobiumanodes. Furthermore, the flammability of the niobium oxides of thepresent invention is significantly lower than the flammability orburning rate of tantalum or niobium, as shown in FIG. 18. The burningrate is determined by Reference Test EEC Directive 79/831 ANNEX Part Afrom Chilworth Technology Inc. Also, the ignition energy (mJ) needed toignite niobium oxide powders is significantly higher than the ignitionenergy needed to ignite niobium powder or tantalum powder as shown inFIG. 19. From such data, the niobium oxide of the present invention didnot ignite at 500 mJ but ignited at an energy level of 10 J (asignificantly higher amount of energy). On the other hand, both niobiumand tantalum powders ignited at less than 3 mJ.

[0046] The capacitor anodes of the present invention which contain theniobium suboxides of the present invention are preferably prepared bypressing niobium oxide powder into the shape of a capacitor anode andsintering the anode at a temperature of from about 1200° C. to about1600° C. for a time of from about 1 minute to about 30 minutes.Afterwards, the anode is then anodized at a formation voltage of fromabout 16 volts to about 75 volts preferably at a formation temperatureof about 85° C. Other formation temperatures can be used such as from50° C. to 100° C. Afterwards, the anode is then annealed at a annealingtemperature of from about 300° C. to about 350° C. for a time of fromabout 10 minutes to about 60 minutes. Once this annealing is completed,the anode is again anodized at the same or slightly lower (5-10% lower)formation voltage than it is exposed to. The second formation lasts fromabout 10 minutes to 120 minutes at about 85° C. The anode is thenpreferably manganized at a temperature of from about 220° C. to about280° C. for a time of from about 1 minute to about 30 minutes.

[0047] The present invention further relates to methods to at leastpartially reduce a niobium oxide. Preferably, the method involves heattreating a starting niobium oxide in the presence of a getter materialin an atmosphere which permits the transfer of oxygen atoms from thestarting niobium oxide to the getter material for a sufficient time anda sufficient temperature to form an oxygen reduced niobium oxide.Preferably, the oxygen reduced niobium oxide is NbO, depleted NbO, or aniobium metal with NbO. As stated earlier, preferably the gettermaterial is a niobium metal and more preferably a niobium powder. In thepreferred process, the getter material converts to the oxygen reducedniobium oxide as well. Thus, the getter material also forms part of thefinal product.

[0048] The present invention will be further clarified by the followingexamples, which are intended to be exemplary of the present invention.TEST METHODS Anode Fabrication: size - 0.197″ dia 3.5 Dp powder wt = 341mg Anode Sintering: 1300° C. 10′ 1450° C. 10′ 1600° C. 10′ 1750° C. 10′30 V Ef Anodization: 30 V Ef @ 60° C./0.1% H₃PO₄ Electrolyte 20 mA/gconstant current DC Leakage/Capacitance - ESR Testing: DC LeakageTesting --- 70% Ef (21 VDC) Test Voltage 60 second charge time 10% H₃PO₄@ 21° C. Capacitance - DF Testing: 18% H₂SO₄ @ 21° C. 120 Hz 50 V EfReform Anodization: 50 V Ef @ 60° C./0.1% H₃PO₄ Electrolyte 20 mA/gconstant current DC Leakage/Capacitance - ESR Testing: DC leakageTesting --- 70% Ef (35 VDC) Test Voltage 60 second charge time 10% H₃PO₄@ 21° C. Capacitance - DF Testing: 18% H₂SO₄ @ 21° C. 120 Hz 75 V EfReform Anodization: 75 V Ef @ 60° C./0.1% H₃PO₄ Electrolyte 20 mA/gconstant current DC Leakage/Capacitance - ESR Testing: DC leakageTesting --- 70% Ef (52.5 VDC) Test Voltage 60 second charge time 10%H₃PO₄ @ 21° C. Capacitance - DF Testing: 18% H₂SO₄ @ 21° C. 120 Hz

[0049] Scott Density, oxygen analysis, phosphorus analysis, and BETanalysis were determined according to the procedures set forth in U.S.Pat. Nos. 5,011,742; 4,960,471; and 4,964,906, all incorporated herebyin their entireties by reference herein.

EXAMPLES Example 1

[0050] +10 mesh Ta hydride chips (99.2 gms) with approximately 50 ppmoxygen were mixed with 22 grams of Nb₂O₅ and placed into Ta trays. Thetrays were placed into a vacuum heat treatment furnace and heated to1000° C. H₂ gas was admitted to the furnace to a pressure of +3psi. Thetemperature was further ramped to 1240° C. and held for 30 minutes. Thetemperature was lowered to 1050° C. for 6 minutes until all H₂ was sweptfrom the furnace. While still holding 1050° C., the argon gas wasevacuated from the furnace until a pressure of 5×10⁴ torr was achieved.At this point 700 mm of argon was readmitted to the chamber and thefurnace cooled to 60° C.

[0051] The material was passivated with several cyclic exposures toprogressively higher partial pressures of oxygen prior to removal fromthe furnace as follows: The furnace was backfilled with argon to 700 mmfollowed by filling to one atmosphere with air. After 4 minutes thechamber was evacuated to 10⁻² torr. The chamber was then backfilled to600 mm with argon followed by air to one atmosphere and held for 4minutes. The chamber was evacuated to 10⁻² torr. The chamber was thenbackfilled to 400 mm argon followed by air to one atmosphere. After 4minutes the chamber was evacuated to 10⁻² torr. The chamber was thembackfilled to 200 mm argon followed by air to one atmosphere and heldfor 4 minutes. The chamber was evacuated to 10⁻² torr. The chamber wasbackfilled to one atmosphere with air and held for 4 minutes. Thechamber was evacuated to 10⁻² torr. The chamber was backfilled to oneatmosphere with argon and opened to remove the sample.

[0052] The powder product was separated from the tantalum chip getter byscreening through a 40 mesh screen. The product was tested with thefollowing results. CV/g of pellets sintered to 1300° C. × 10 minutes andformed to 35 volts = 81,297 nA/CV (DC leakage) = 5.0 Sintered Density ofpellets = 2.7 g/cc Scott density = 0.9 g/cc Chemical Analysis (ppm) C =70 H₂ = 56 Ti = 25 Mn = 10 Sn = 5 Cr = 10 Mo = 25 Cu = 50 Pb = 2 Fe = 25Si = 25 Ni = 5 Al = 5 Mg = 5 B = 2 all others < limits

Example 2

[0053] Samples 1 through 20 are examples following similar steps asabove with powdered Nb₂O₅ as indicated in the Table. For most of theexamples, mesh sizes of the starting input material are set forth in theTable, for example 60/100, means smaller than 60 mesh, but larger than100 mesh.

[0054] Similarly, the screen size of some of the Ta getter is given as14/40. The getters marked as “Ta hydride chip” are +40 mesh with noupper limit on particle size.

[0055] Sample 18 used Nb as the getter material (commercially availableN200 flaked Nb powder from CPM). The getter material for sample 18 wasfine grained Nb powder which was not separated from the final product.X-ray diffraction showed that some of the getter material remained asNb, but most was converted to NbO_(1.1) and NbO by the process as wasthe starting niobium oxide material Nb₂O₅.

[0056] Sample 15 was a pellet of Nb₂O₅, pressed to near solid density,and reacted with H₂ in close proximity to the Ta getter material. Theprocess converted the solid oxide pellet into a porous slug of NbOsuboxide. This slug was sintered to a sheet of Nb metal to create ananode lead connection and anodized to 35 volts using similar electricalforming procedures as used for the powder slug pellets. This sampledemonstrates the unique ability of this process to make a ready toanodize slug in a single step from Nb₂O₅ starting material.

[0057] The Table shows the high capacitance and low DC leakage capableof anodes made from the pressed and sintered powders/pellets of thepresent invention. Microphotographs (SEMs) of various samples weretaken. These photographs show the porous structure of the reduced oxygenniobium oxide of the present invention. In particular, FIG. 1 is aphotograph of the outer surface of a pellet taken at 5,000 X (sample15). FIG. 2 is a photograph of the pellet interior of the same pellettaken at 5,000 X. FIGS. 3 and 4 are photographs of the outer surface ofthe same pellet at 1,000 X. FIG. 5 is a photograph of sample 11 at 2,000X and FIGS. 6 and 7 are photographs taken of sample 4 at 5,000 X. FIG. 8is a photograph taken of sample 3 at 2,000 X and FIG. 9 is a photographof sample 6 at 2,000 X. Finally, FIG. 10 is a photograph of sample 6,taken at 3,000 X and FIG. 11 is a photograph of sample 9 taken at 2,000X. TABLE 1 Hydro- gen XRD* XRD* XRD* XRD* Sam- Temp Time Pres- MajorMajor Minor Minor 1300X35v 1300X35v ple Input Material Gms Input GetterGms (° C.) (min) sure 1** 2*** 1*** 2*** CV/g na/CV 1 −40 mesh 20 Tahydride chips 40 1240 30 3 psi 81297 5 calcined Nb₂O₅ (est) (est) 260/100 Nb₂O₅ 23.4 Ta hydride chips 65.4 1250 30 3 psi NbO_(1.1) NbO TaO115379 1.28 3 60/100 Nb₂O₅ 23.4 Ta hydride chips 65.4 1250 30 3 psiNbO_(1.1) NbO TaO 121293 2.19 4 100/325 Nb₂O₅ 32.3 Ta hydride chips 92.81250 30 3 psi 113067 1.02 5 100/325 Nb₂O₅ 32.3 Ta hydride chips 92.81250 30 3 psi 145589 1.42 6 60/100 Nb₂O₅ 26.124 Ta hydride chips 72.3491250 90 3 psi 17793 12.86 7 60/100 Nb₂O₅ 26.124 Ta hydride chips 72.3491250 90 3 psi 41525 5.63 8 200/325 Nb₂O₅ 29.496 Ta hydride chips 83.4151250 90 3 psi 17790 16.77 9 60/100 Nb₂O₅ 20.888 Ta hydride chips 60.7671200 90 3 psi NbO_(1.1) NbO Ta₂O₅ 63257 5.17 10 60/100 Nb₂O₅ 20.888 Tahydride chips 60.767 1200 90 3 psi NbO_(1.1) NbO Ta₂O₅ 69881 5.5 11200/325 Nb₂O₅ 23.936 Ta hydride chips 69.266 1200 90 3 psi NbO_(1.1) NbOTa₂O₅ 61716 6.65 12 200/325 Nb₂O₅ 23.936 Ta hydride chips 69.266 1200 903 psi NbO_(1.1) NbO Ta₂O₅ 68245 6.84 13 200/325 Nb₂O₅ 15.5 14/40 Tahydride 41.56 1250 30 3 psi NbO_(0.7) NbO TaO NbO₂ 76294 4.03 14 200/325Nb2O5 10.25 14/40 Ta hydride 68.96 1250 30 3 psi NbO_(0.7) NbO TaO NbO₂29281 21.03 15 Nb₂O₅ pellets 3.49 14/40 Ta hydride 25.7 1250 30 3 psi70840 0.97 16 200/325 Nb₂O₅ 13.2 14/40 Ta hydride 85.7 1200 30 3 psiNbO₂ NbO_(0.7) TaO NbO 5520 34.33 17 200/325 Nb₂O₅ 14.94 14/40 Tahydride 41.37 1200 30 3 psi 6719 38.44 18 200/325 Nb₂O₅ 11.92 N200 Nbpowder 21.07 1200 30 3 psi Nb NbO_(1.1) NbO 25716 4.71 19 200/325 Nb₂O₅10 14/40 Ta hydride 69 1250 30 100 108478 1.95 Torr 20 200/325 Nb₂O₅ 1614/40 Ta hydride 41 1250 30 100 106046 1.66 Torr

Example 3

[0058] This experiment was conducted to show the ability of the niobiumoxides of the present invention to form at high formation voltages andyet retain an acceptable DC leakage. The niobium oxide of the presentinvention was compared to a capacitor formed from commercially availabletantalum and niobium metal. In particular, Table 2 sets forth the basiccharacteristics of the materials that were used to form the capacitorfor this example. The C606 tantalum is a commercially available productfrom Cabot Corporation. The niobium oxide used in Example 3 was preparedin manner similar to Example 1. Table 3 further set forth the chemicalcompositions of components other than the niobium metal for the niobiumoxide of the present invention and the niobium metal which was used forcomparison purposes. Tables 4-7 set forth the data obtained for eachformation voltage starting at 15 volts and ending at 75 volts. The datais also plotted in FIG. 12. The particular capacitor anodes which weretested for DC leakage were formed using the stated formation voltage andin each case the sintering temperature was 1300° C. for 10 minutes andthe formation temperature of the anode was 60° C. with the press densityset forth in Table 2. Further, the anodes were formed in 0.1% H₃PO₄electrolyte, with a 135 milliamps/g constant current up to the desiredformation voltage which was held for 3 hours. The test conditions werethe same as for the DC leakage tested in Example 1 (except as notedherein) including 10% H₃PO₄ at 21° C. The anode size of the Nb suboxidewas 0.17 inch diameter. The anode size of the tantalum was 0.13 inchdiameter and the anode size for the niobium was 0.19 inch diameter. Theanode weight was as follows: niobium suboxide=200 mg; tantalum=200 mg;niobium=340 mg. TABLE 2 Ta C606 Nb Sub-Oxide Nb (Commercial product)BET, m²/g 0.75 0.58 Commercial spec Scott density, g/in² 20.7 23.8Commercial spec Anode sintering 3.0 4.1 5.3 density, g/cc CV/g 56,56222,898 61,002 Sintering conditions 10 min @ 10 min @ 10 min @ 1300° C.1300° C. 1300° C. Formation 60° C. 60° C. 60° C. temperature

[0059] TABLE 3 Element Nb Oxide Nb C 150 422 O 141,400 2399 H 55 Si 30250 Ni 10 20 Fe 200 100 Cr 40 50 Ti <5 <5 Mn 25 25 Sn <5 <5 Ca <50 <50Al 50 20 W <100 <100 Zr <5 <5 Mg 25 10 B <5 10 Co <5 <5 Cu <5 10

[0060] As can be seen in FIG. 12 and Tables 4-7, while the DC leakagefor capacitor anodes made from niobium metal increased dramatically at aformation voltage of 75 volts, the DC leakage for the capacitor anodeformed from a niobium oxide of the present invention remain relativelystable. This is quite impressive considering the effect seen withrespect to a capacitor anode formed from niobium metal. Thus, unlikeniobium metal, the niobium oxides of the present invention have theability to be formed into capacitor anodes and formed at high voltageswhile maintaining acceptable DC leakage which was not possible withanodes made simply from niobium metal. Thus, the niobium oxides of thepresent invention can be possible substitutes for anodes made fromtantalum in certain applications which is quite beneficial consideringniobium can be less expensive. TABLE 4 Nb Sub-Oxide Ta Ta Nb Anodization15.0 15.0 15.0 15.0 Voltage (CV) 11,037 13,095 12,635 7,893 (CV/g)56,562 63,154 61,002 22,898 (CV/g) (Corr) (CV/cc) 168,304 352,254324,448 93,372 (Ohms) 0.82 0.92 0.90 0.89 Charge time 30 30 30 30 one(sec) (uA) 72.86 10.94 12.74 13.14 *“FLIERS” 0 0 0 0 “GASSERS” 0 0 0 0N= 8 8 8 2 (uA/g) 373.37 52.75 61.51 38.12 (nA/CV) 6.60 0.84 1.01 1.66Charge time 60 60 60 60 two (sec) (uA) 60.08 7.39 9.00 9.42 “FLIERS” 0 00 0 “GASSERS” 0 0 0 0 N= 8 8 8 2 (uA/g) 307.90 35.63 43.45 27.31 (nA/CV)5.44 0.56 0.71 1.19 Dia. Shkg (%) 0.6 0.6 −1.2 4.0 Ds (g/cc) 3.0 5.6 5.34.1

[0061] TABLE 5 Nb Sub-Oxide Ta Ta Nb Anodization 35.0 35.0 35.0 35.0Voltage (CV) 10,445 12,678 12,130 7,977 (CV/g) 53,107 60,470 58,44823,457 (CV/g) (Corr) (CV/cc) 158,416 341,045 311,482 93,700 (Ohms) 0.921.04 1.02 0.95 Charge time 30 30 30 30 one (sec) (uA) 54.13 11.50 29.6053.31 *“FLIERS” 0 1 0 0 “GASSERS” 0 0 0 0 N= 8 8 8 2 (uA/g) 275.23 54.86142.64 156.77 (nA/CV) 5.18 0.91 2.44 6.68 Charge time 60 60 60 60 two(sec) (uA) 47.21 7.56 20.99 31.17 “FLIERS” 0 1 0 0 “GASSERS” 0 0 0 0 N=8 8 8 2 (uA/g) 240.04 36.08 101.14 91.66 (nA/CV) 4.52 0.60 1.73 3.91Dia. Shkg (%) 0.6 0.6 −1.2 3.8 Ds (g/cc) 3.0 5.6 5.3 4.0

[0062] TABLE 6 Nb Sub-Oxide Ta Ta Nb Anodization 55.0 55.0 55.0 55.0Voltage (CV) 9,476 11,448 10,878 7,894 (CV/g) 47,159 54,928 52,39422,941 (CV/g) (Corr) (CV/cc) 134,774 307,960 279,339 92,880 (Ohms) 1.351.21 1.18 1.08 Charge time 30 30 30 30 one (sec) (uA) 53.70 13.48 28.4061.61 *“FLIERS” 0 0 0 0 “GASSERS” 0 0 0 0 N= 8 8 8 2 (uA/g) 267.23 64.65136.80 179.05 (nA/CV) 5.67 1.18 2.61 7.80 Charge time 60 60 60 60 two(sec) (uA) 46.28 8.91 20.24 36.29 “FLIERS” 0 0 0 0 “GASSERS” 0 0 0 0 N=8 8 8 2 (uA/g) 230.34 42.77 97.50 105.45 (nA/CV) 4.88 0.78 1.86 4.60Dia. Shkg (%) 0.3 0.6 −1.2 3.8 Ds (g/cc) 2.9 5.6 5.3 4.0

[0063] TABLE 7 Nb Sub-Oxide Ta Ta Nb Anodization 75.0 75.0 75.0 75.0Voltage (CV) 5,420 10,133 9,517 7,872 (CV/g) 27,508 48,484 45,749 22,886(CV/g) (Corr) (CV/cc) 80,768 274,194 246,127 93,954 (Ohms) 4.58 1.371.31 1.31 Charge time 30 30 30 30 one (sec) (uA) 67.08 16.76 27.47640.50 *“FLIERS” 0 0 0 0 “GASSERS” 0 0 0 0 N= 8 8 8 2 (uA/g) 340.4080.17 132.04 1862.19 (nA/CV) 12.37 1.65 2.89 81.37 Charge time 60 60 6060 two (sec) (uA) 55.91 10.97 19.90 412.20 “FLIERS” 0 0 0 0 “GASSERS” 00 0 0 N= 8 8 8 2 (uA/g) 283.75 52.48 95.67 1198.43 (nA/CV) 10.32 1.0820.9 52.37 Dia. Shkg (%) 0.1 0.9 −0.9 4.3 Ds (g/cc) 2.9 5.7 5.4 4.14

[0064] Other embodiments of the present invention will be apparent tothose skilled in the art from consideration of the specification andpractice of the invention disclosed herein. It is intended that thespecification and examples be considered as exemplary only, with a truescope and spirit of the invention being indicated by the followingclaims.

What is claimed is:
 1. A capacitor anode comprising a niobium oxidehaving an atomic ratio of niobium to oxygen of 1: less than 2.5 andbeing formed at a formation voltage of about 6 volts or higher, andhaving a DC leakage of less than 15 nA/CV wherein said DC leakage isdetermined from an anode sintered at 1500° C. for 10 minutes and formedat a formation voltage of 60° C.
 2. The capacitor anode of claim 1 ,wherein said DC leakage is less than about 12 nA/CV.
 3. The capacitoranode of claim 1 , wherein said DC leakage is less than 6 nA/CV.
 4. Thecapacitor anode of claim 1 , wherein said DC leakage is less than 2nA/CV.
 5. The capacitor anode of claim 1 , wherein said niobium oxide isNbO.
 6. The capacitor anode of claim 1 , wherein said niobium oxide isNbO, oxygen depleted NbO, niobium metal with NbO, or combinationsthereof.
 7. A capacitor anode comprising a niobium oxide having anatomic ratio of niobium to oxygen of 1: less than 2.5, and being formedat a formation voltage of about 6 volts or higher, and having acapacitance of 40,000 CV/g or greater at a sintering temperature of fromabout 1200° C. to about 1600° C. for 10 minutes and at a formationtemperature of 85° C.
 8. The capacitor anode of claim 7 , wherein saidcapacitance is from about 40,000 to about 60,000 CV/g.
 9. The capacitoranode of claim 7 , wherein said niobium oxide is NbO.
 10. The capacitoranode of claim 7 , wherein said niobium oxide is NbO, oxygen depletedNbO, niobium metal with NbO, or combinations thereof.
 11. A capacitoranode comprising a niobium oxide having an atomic ratio of niobium tooxygen of 1: less than 2.5, and being formed at a formation voltage ofabout 6 volts or higher and having a capacitance of 20,000 CV/g orgreater, wherein said capacitance is determined at a sinteringtemperature of 1300° C. for 10 minutes and at a formation temperature of85° C.
 12. The capacitor anode of claim 11 , wherein said capacitance isfrom about 20,000 to about 60,000 CV/g.
 13. The capacitor anode of claim11 , wherein said formation voltage is from about 20 to about 80 volts.14. The capacitor anode of claim 11 , wherein said niobium oxide is NbO.15. The capacitor anode of claim 11 , wherein said niobium oxide is NbO,depleted NbO, niobium metal with NbO, or combinations thereof.
 16. Acapacitor anode comprising a niobium oxide having an atomic ratio ofniobium to oxygen of 1: less than 2.5, wherein the powder forming thecapacitor anode has a burning rate of less than 5 mm/s.
 17. Thecapacitor anode of claim 16 , wherein said burning rate is 2 mm/s orlower.
 18. The capacitor anode of claim 16 , wherein said burning rateis about 1 mm/s to about 5 mm/s.
 19. A capacitor anode comprising aniobium oxide having an atomic ratio of niobium to oxygen of 1: lessthan 2.5, and having a minimum ignition energy of 100 mJ or greater. 20.The capacitor anode of claim 19 , wherein said minimum ignition energyis 500 mJ or greater.
 21. The capacitor anode of claim 19 , wherein saidminimum ignition energy is below 10 J.
 22. The capacitor anode of claim19 , wherein said niobium oxide is NbO.
 23. The capacitor anode of claim19 , wherein said niobium oxide is NbO, oxygen depleted NbO, niobiummetal with NbO, or combinations thereof.
 24. A method of forming acapacitor anode comprising a niobium oxide having an atomic ratio ofniobium to oxygen of 1: less than 2.5, comprising forming said niobiumoxide into the shape of an anode and sintering at a temperature of fromabout 1200° C. to about 1600° C. for a time of from about 1 minute toabout 30 minutes; anodizing at from about 16 to about 75 volts at aformation temperature of about 85° C.; annealing said anode at atemperature of from about 300 to about 350° C. for a time of from about10 minutes to about 60 minutes; and manganizing said anode at atemperature of from about 220 to 280° C.
 25. A method to at leastpartially reduce a niobium oxide, comprising heat treating a startingniobium oxide in the presence of a getter material in an atmospherepermitting the transfer of oxygen atoms from the starting niobium oxideto the getter material for a sufficient time and sufficient temperaturesuch that the starting niobium oxide and said getter material form anoxygen reduced niobium oxide.
 26. The method of claim 25 , wherein saidgetter material is a niobium powder.
 27. The method of claim 25 ,wherein said oxygen reduced niobium oxide is NbO.
 28. The method ofclaim 25 , wherein said oxygen reduced niobium oxide is NbO, oxygendepleted NbO, niobium metal with NbO, or combinations thereof.
 29. Themethod of claim 25 , wherein said atmosphere is a hydrogen containingatmosphere.
 30. The method of claim 25 , wherein said atmosphere ishydrogen.
 31. The method of claim 25 , wherein said heat treating occursat a temperature of from about 800° C. to about 1900° C. for a time offrom about 5 minutes to about 100 minutes.